1. Field of the Invention
The invention relates to an air conditioning apparatus including multiple outdoor units and multiple indoor units connected by multiple refrigerant pipes and, more specifically, it relates to such air conditioning apparatus capable of preventing a shortage of refrigerant unit oil within a compressor.
2. Related Art
Conventionally, there is proposed an air conditioning apparatus in which multiple indoor units are parallel connected to at least one outdoor unit by multiple refrigerant pipes and the respective indoor units can execute a cooling operation and a heating operation. For example, the patent reference 1 discloses an air conditioning apparatus of a so called cooling and heating free operation type in which two indoor units are parallel connected to an outdoor unit including two outdoor heat exchangers by a high pressure gas pipe, a low pressure gas pipe and a liquid pipe, and the two indoor units can independently execute a heating operation and a cooling operation selectively.
In the above air conditioning apparatus, the number of outdoor heat exchangers equipped in the outdoor unit is selected according to the operation capacity required of the two indoor units. When the operation capacity required of the two indoor units is low, one of the outdoor heat exchangers is used and, when the required capacity is high, both heat exchangers are used.
When the above air conditioning apparatus is installed in a cold district, or when the open-air temperature is low (for example, it is 0° C. or lower), for example, in the early morning or in the middle of the night in winter, there is a fear that, while the air conditioning apparatus is not in operation, a state where a refrigerant is dissolved in the refrigerating machine oil of a compressor, namely, so-called refrigerant dissolution can occur within a compressor provided in the outdoor unit.
When, in the refrigerant dissolution state, the operation of the air conditioning apparatus is started and the compressor is actuated, the refrigerant dissolved in the refrigerating machine oil evaporates to a gas refrigerant. When this gas refrigerant is discharged to the outside of the compressor, it catches and takes out the refrigerating machine oil to the outside of the compressor, thereby causing a shortage of the refrigerating machine oil within the compressor. This raises a fear that the poor lubrication of the compressor can occur.
Therefore, in an ordinary air conditioning apparatus, the rotation number of the compressor in its start time is controlled to a given rotation number previously determined for warming the compressor and, while maintaining this rotation number, the compressor is driven on for a given period of time to thereby eliminate the refrigerant dissolution within the compressor.
That is, by executing the above start control, the refrigerant dissolution, which had occurred in the start time of the compressor before, is eliminated to restrict the amount of the refrigerating machine oil to be taken out to the outside of the compressor by the gas refrigerant, thereby preventing the poor lubrication of the compressor.